A friend of mine in PA emailed me asking for help.
I nearly never use patterns anymore and my best guess was that "M.1" referred top "pick up horizontal yarn between 2 sts and knit twisted".
Here's what she wrote:

". . . in this case the M.1 was to refer to the little chart labeled M.1 in the pattern. It looked like you are supposed to do yarn over but I don’t see how you can do that without something in between. I think I just don’t understand the chart. . . "

I don't know which item she is making but I actually knit the little sweater in this set. It is a real favorite of mine, it turned out so cute.

The M.1 chart is worked over 17 stitches and row 1 is: (K2tog) 3 times, (YO, K1) 5 times, YO, (K2tog) 3 times. Remind her that the charts show everything from the right side, so the right side will have this row and then a line of garter stitch and then 2 rows of St st.

I don't know which item she is making but I actually knit the little sweater in this set. It is a real favorite of mine, it turned out so cute.

The M.1 chart is worked over 17 stitches and row 1 is: (K2tog) 3 times, (YO, K1) 5 times, YO, (K2tog) 3 times. Remind her that the charts show everything from the right side, so the right side will have this row and then a line of garter stitch and then 2 rows of St st.

Thank you!

I finally dragged myself away from my finishing work and scrolled down far enough to see the charts.
I had just emailed her exactly what you said. Thanks for the additional hint on reading the charts.

I was just remarking to a fellow knitter yesterday about the lack of uniformity in knitting charts.

It is a darling pattern.

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*Knit, rip*, repeat between the *s as many times as necessary.